1. Field of the Invention
The present invention relates to tooling apparatus. More specifically, the present invention relates to devices used to clamp work pieces during manufacturing operations.
While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility.
2. Description of the Related Art
In many applications, a clamp is needed to hold two work pieces in position to perform a manufacturing operation. In automotive manufacturing, for example, a number of structural members must be held together and welded to construct a skeletal structure or framework commonly referred to as a "body in white". Most manufacturers use a numerically controlled machined block as a clamp at every point at which the structural members must be held together during the welding operation. While this provides a consistent, reliable, durable clamping arrangement, it is quite costly. For every model or design of vehicle, a specific customized clamp or numerically machined block must be provided for every welding point of the `body in white`. The design and manufacture of the clamps is costly and time consuming. For example, it may require one and one-half years to design and manufacture the tooling necessary to manufacture a given vehicle. A typical factory may spend 400 to 600 dollars for each numerically machined block. With each subassembly having 20 to 30 blocks and 30 to 40 subassemblies for each vehicle design, with three or four machines making each subassembly, the cost associated with the conventional clamping tool is substantial. These costs are not transferable and are generally lost when the model is discontinued.
Thus, a need has been recognized in the art for reusable, reconfigurable clamps. U. S. Pat. No. 4,691,905, entitled MACHINE FOR HOLDING WORKPIECE, issued Sep. 8, 1987 to Tamura et al., describes several methods for fixturing vehicle frames prior to the performance of a manufacturing operation. While a programmable fixture is disclosed, it has several disadvantages. Firstly, it is trained or contoured to the part with actuators and actuator controls (typically servo-motors) which are costly, unreliable and imprecise. In addition, the positioning manipulator must carry the weight and size of the actuators along with the tooling, requiring larger, stronger, more costly manipulators.
Secondly, while individual plates are used to reconfigure the clamp, the disclosed clamp is only two dimensional in that it allows contouring with only two degrees of freedom. Accordingly, it can only be contoured to a limited set of vehicle components.
Thirdly, the constant width of the plates restricts the fixture from obtaining shapes necessary for fixturing at tooling holes and slots commonly known as principle locating points. Hence, the clamp cannot generally be used to precisely locate the part in space. This is significant because it requires that the parts be presented in the correct position and orientation or that a sensor system be used to locate the position of the part. Both result in higher tooling costs and lower overall framing accuracy.
Thus, a need remains in the art for an inexpensive, reliable, durable, reusable, reconfigurable clamp which allows contouring with more than two degrees of freedom, which may be inexpensively customized, provides accurate part location, and which does not require servo-motors for training.